Effect of Water Activity and Titania P25 Photocatalyst on Inactivation of Pathogenic Fungi--contribution to the Protection of Public Health.

AIM The aim of this study was to determine the antifungal activity of titanium dioxide activated by indoor light on Czapek Yeast Agar (CYA). METHODS The agar plate method was used and titania P25 (Evonik) was added to the medium in the amount of 20 g.dm(-3). The control experiments without titania were also carried out. The water activity (a(w)) of the basal media was adjusted to 0.999, 0.997, 0.975, 0.950, 0.900 and 0.850 with sodium chloride. The photoactivity of titania was tested for six strains of potentially pathogenic fungi: Aspergillus versicolor (WB130, W11), Stachybotrys chartarum (STA1), Pseudallescheria boydii (AP25), Pseudallescheria ellipsoidea (ZUT1 2), Scedosporium apiospermum (ZUT1 1), Scedosporium aurantiacum (ZUT4BIS). After inoculation with fungal spore suspensions, one part of CYA plates was incubated in dark, while another part was daily exposed to indoor light for 12 hours per day.The plates were incubated at 25°C for 10 days. The daily growth rates (mm x day(-1)) were calculated from the linear regression equation. RESULTS The CYA supplementation with titanium dioxide for different availability of water resulted in the decrease of fungal growth rates in dark and under irradiation. The lowest and the highest rates of daily growth were obtained in the presence and absence of titania for the low and high water activity (0.900 a(w) and 0.999 a(w)), respectively. CONCLUSIONS Fungi did not grow on all examined media with the lowest water activity (a(w) ≤ 0.850) which confirmed necessity of water for their growth. The fungi Pseudallescheria-Scedosporium were the most sensitive to titania and water activity, while the strains of Aspergillus versicolor were the most resistant to the presence of titania and lack of water. It has been shown that the lack of accessible water resulted in the strongest action of titanium dioxide both in dark and under irradiation. For the lowest amount of accessible water irradiation of titania resulted in complete inhibition of fungal growth. While, under dark conditions, titania presence enhanced the growth of persistent fungi, i.e., Aspergillus versicolor. It is assumed that these fungi could obtain water from the water-rich titania surface.